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# arrow

An arrow is a line, usually straight, capped at one end, or both ends, with an arrowhead which points in a specific direction. In a flowchart, arrows show the order in which instructions are to be performed (including where branching may occur) or they show the flow of cause and effect. In certain arrangements of numbers, such as the Collatz tree, arrows show which numbers are the input values, with the output value being pointed at by the arrowhead.

In writing about vectors, arrows can be written over the symbols for the origin and the endpoint, e.g., $\overrightarrow{AB}$ and $\overleftarrow{CD}$. TeX provides commands for these.

An arrow, regarded as a morphism, functor or natural transformation also plays central roles in Category Theory and Categorical Dynamics.

## Mathematics Subject Classification

00A99*no label found*

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## Comments

## Original Content Altered Completely

The original author of this entry did not intend this entry to be on the common usage of "arrow". Please restore this perfectly legitimate and well-written entry to its original state... and add a reference, as suggested.

If you want to add an entry on "arrow" in its common usage, please create a separate entry for it.

## Re: Original Content Altered Completely

The original author should have foreseen what would happen if he forgot to log in to PlanetMath for a long while. I can't find a reference at the moment and doubt there is one to be found. But if perchance such a reference is found, the original author's entry will be restored under a different canonical name, one that is less prone to irrelevant autolinking.